Grignard reaction of cyanoalkylsilanes in the presence of tertiary amines



United States Patent GRIGNARD REACTION OF CYANOALKYLSIL- ANES IN THEPRESENCE OF TERTIARY AMINES Maurice Prober, Schenectady, N.Y., assignorto General Electric Company, a corporation of New York No Drawing.Application May 20, 1957 Serial No. 660,074

6 Claims. (Cl. 260-4482) This invention relates to a process forsubstituting a hydrocarbon radical for a silicon-bonded hydrolyz 'ableradical of an organopolysiloxane containing both a siliconbondedcyanoalkyl radical and a silicon-bonded hydrolyzable radical.

In recent years organosilicon compounds have obtained wide commercialacceptance as industrial materials because of the superior thermalstability of these compounds over conventional organic materials. Theseorganosilicon compounds may be converted into polymeric materials whichare useful as lubricants, lubricant additives, elastomers, and resins.Among the newer organosilicon compounds are hydrolyzable silanescontaining one or more silicon-bonded, cyanoalkyl radicals. Hydrolyzablesilanes containing silicon-bonded cyanoalkyl radicals may be convertedby conventional means into polymeric fluids, resins and elastomers withlubricating, solvent resistance and physical properties superior to theproperties of corresponding organopolysiloxanes in which all of theorgano groups are hydrocarbon radicals.

In order toobtain a full spectrum of organosilicon compounds andorgauopolysiloxanes containing a siliconbonded cyanoalkyl radical, it isnecessary to have as starting materials organosilicon compoundscontaining at least one cyanoalkyl radical and a number ofsilicon-bonded hydrolyzable radicals which varies from 0 to 3. The needfor the variable number of hydrolyzable silicon-bonded radicals occursbecause each type of organosilane is particularly valuable in theformation of a particular type of end product. Thus, organosiliconcompounds containing threesilicon-bonded hydrolyzable radicals areparticularly valuable in theformation of organopolysiloxane resins.Those compounds containing two silicon-bonded hydrolyzable radicalsareparticularly valuable in the formation of organopolysiloxane elastomers.Those compounds containing one hydrolyzable radical are particularlyvaluable in the formation of linear chain-stopped organopolysiloxanefluids.

In order to have a full spectrum of organosilicon compounds available,it is convenient to have one type of hydrolyzable organosilicon compoundavailable which .mayv beconverted to other hydrolyzable organosiliconcompounds with a different number of silicon-bonded hydrolyzable groups.Thus, it is very desirable to have as an:.available starting material anorganosilicon compound containing three hydrolyzable groups. and to havea method for the conversion of this compound to other organosiliconcompounds containing fewer hydrolyzable I groups.

In the past it has been possible to convert an organosilicon compoundsuch as methyltrichlorosilane to dimethyldichlorosilane ortrimethylchlorosilane by reacting methyltrichlorosilane withv a methylGrignard reagent which serves to alkylate the silicon atom. However,when an attempt is made to alkylate a compound containingasilicon-bonded cyanoalkyl radical, such as, for example,S-cyanoethyltrichlorosilane, the presence of the nitrile radical in thecompound interferes with the alkyla- 2,913,472 Patented Nov. 17, 1959 2.tion and results in a very poor yield of products such asmethyl-p-cyanoethyldichlorosilane anddimethyl-fl-cyanoethylchlorosilane.

It is' an object of this invention to provide a process wherein ahydrocarbon radical may be substituted for a silicon-bonded hydrolyzableradical on an organosilicon compound containing both a cyanoalkylradical and a silicon-bonded hydrolyzable radical.

This and other objects of my invention are accomplished by my processfor substituting a hydrocarbon radical for the hydrolyzable group of anorganopolysiloxane containing both a silicon-bonded cyanoalkyl radicaland a silicon-bonded hydrolyzable radical, which process compriseselfecting reaction between the hydrolyzable silane and a Grignardreagent, such as a hydrocarbonyl magnesium halide, in the presence of atertiary amine.

The hydrolyzable cyanoalkyl silanes to which my process is applicablecan be described generally as containing at least one silicon-bondedcyanoalkyl radical, at least one silicon-bonded hydrolyzable radical,with the remaining valences of silicon being satisfied by hydrocarbonradicals. These compounds are more particularly described by thefollowing formula:

where X represents a hydrolyzable group selected from the classconsisting of halogen, e.g., chlorine, bromine, iodine; acyloxyradicals, e.g., acetoxy, propionoxy, etc. radicals, alkoxy radicals,e.g., lower alkoxy radicals such as methoxy, ethoxy, propoxy, butoxy,heptoxy, etc. radicals, aryloXy radicals, e.g., phenoxy,alkyl-substituted phenoxy radicals, etc., R is a monovalent hydrocarbonradical, such as a lower alkyl radical, e.g., methyl, ethyl, propyl,butyl, heptyl, cyclohexyl, etc. radicals; an aryl radical, e.g., phenyl,naphthyl, diphenyl, tolyl, Xylyl, etc. radicals; or an aralkyl radical,e.g., benzyl, phenyl ethyl, etc. radical; R is a saturated divalentaliphatic hydrocarbon radical having from 1 to 7 carbon atoms, e.g.,methylene, ethylene, propylene, isopropylene, ethylidine, etc. radicals;a is a whole number having a value from 1 to 3, inclusive; b is a wholenumber having a value of from 0 to 2, inclusive; and the sum of a+b is awhole number equal to from 1 to-"3, inclusive.

The hydrolyzable cyanoalkyl silanes within the scope of Formula 1 abovemay be prepared by a number of diflf erent methods. The most convenientmethod for preparing compounds within the scope of the formula whichcontain a silicon-bonded fi-cyanoalkyl radical is the metlr od describedin my copending application Serial No. 401,- 702, filed December 31,1953, and assigned to the same assignee as the present invention. In themethod described in this copending application an organosilicon compoundcontaining both silicon-bonded halogen and siliconbonded hydrogen isadded across the double bond of acrylonitrile or alkyl-substitutedacrylonitrile in the presence of a tertiary alkyl amine. This results ina B-cyano alkyl halogenosilane. For example,fl-cyanoethyltrichlorosilane may be prepared by reacting trichlorosilanewith acrylonitrile in the presence of tributylamine. Methyl--cyanopropyldichlorosilane may be prepared by reactingmethyldichlorosilane with methylacrylonitrile in the presence oftributyl amine. These halogenosilanes may be converted to thecorresponding.alkoxysilane,raryloxysilane or acyloxysilane by reactionwith a suitable alcohol, phenol, or organic acid salt.

Another method for forming the cyanoalkyl hydrolyzable silanes withinthe scope of Formula 1 is by the peroxide catalyzed addition of anorganosilicon compound containing both silicon-bonded halogen andsiliconbonded hydrogen to a cyanoalkene. Thus,w-cyanobutyltrichlorosilane may be prepared by effecting reactionbetween .rtrichlorosilaneland' 4-.cyanobutene -lt in the preselice of aperoxide such as benzoyl peroxide or acetyl peroxide. Generally, thisreaction is carried out at an elevated temperature in a bomb,temperatures of from ISO-300 C. being satisfactory for the addition.

The hydrocarbonyl magnesium halides employed in the practice of thepresent invention are conventional Grignard reagents which have thegeneral formula R"Mg where R" represents a hydrocarbon radical selectedfrom the class consisting of lower alkyl radicals and aryl radicals,e.g., methyl, ethyl, propyl, butyl, heptyl, phenyl, benzyl, xylyl, etc.radicals; and Z is halogen, e.g., bromine, chlorine or iodine. TheseGrignard reagents are prepared by reacting a hydrocarbon halide of theformula where R" and Z are as defined above with magnesium turnings inan ether solution by conventional methods. The tertiary amines which maybe employed in the process of this invention are generally hydrocarbonamines containing only carbon, hydrogen and nitrogen. Suitable aminesinclude trialkyl amines such as trimethyl amine, triethyl amine,tributyl amine, dimethylethyl amine, dimethylcyclohexyl amine; triarylamines, such as triphenyl amine, tritolyl amine, trinaphthyl amine;alkylaryl amines, e.g., dimethyl phenyl amine, benzyldimethyl amine,butyldiphenyl amine, etc.; heterocyclic amines, e.g., pyridine,quinoline, N-substituted piperidine such as N-methyl piperidine;diamines, e.g., N,N,N',N'-tetramethylethylenediamine, etc. In addition,tertiary amines within the scope of the present invention include aminescontaining atoms other than carbon, hydrogen and nitrogen where theother atoms do not affect the characteristics of the amine. An exampleof this type of amine is N-ethylmorpholine.

The reaction of the present invention is effected by merely mixing thehydrolyzable cyanoalkyl silane of Formula 1 with the Grignard reagent ofFormula 2 and the tertiary amine. The net effect of the reaction is toreplace one or more of the silicon-bonded hydrolyzable groups of thesilane of Formula 1 with the hydrocarbon radical which is present in theGrignard reagent of Formula 2. A typical illustration of a reactionwithin the scope of the present invention is the reaction ofB-cyanoethyltrichlorosilane with methyl magnesium bromide in thepresence of quinoline. The result of this reaction is to substitute oneor more methyl radicals for the silicon-bonded chlorine atoms of thechlorosilane. Thus, products of the reaction aremethyl-B-cyanoethyldichlorosilane, di-

methyl-[3-cyanoethylchlorosilane, and trimethyl-fl-cyanoethylsilane. Asa general rule, the reaction of the present invention leads to thesubstitution of only one of the silicon-bonded hydrolyzable radicals ofthe cyanoalkyl hydrolyzable silane. However, by-products of the reactionsometimes include products in which more than one of the silicon-bondedhydrolyzable radicals are replaced by hydrocarbon radicals.

The ratio of the ingredients employed in the process of the presentinvention may vary within fairly wide limits. However, it is preferredto have present equimolar amounts of the cyanoalkyl hydrolyzable silane,the Grignard reagent and the teriary amine. Satisfactory reactions arealso obtained when the amount of Grignard reagent present is less than 1mole per mole of the tertiary amine or of the cyanoalkyl hydrolyzablesilane. Where less than 1 mole of the Grignard reagent is employed, Iprefer to employ not less than one-half mole of the Grignard reagent permole of the cyanoalkyl hydrolyzable silane. The amount of tertiary aminepresent in the reaction mixture may comprise more than one mole per moleof the Grignard reagent, for example, up to 2 moles of the tertiaryamine per mole of the Grignard reagent.

In carrying out the reaction of the present invention, it is convenienttoemp-loy a solvent for the reaction mixture., Since the Grignardreagents are conventionally formed in diethyl ether, we prefer to usediethyl ether as the reaction solvent. The amount of solvent present perpart of reactants is not at all critical. Generally, I employ forconvenience about 1 to 100 parts, by weight, of solvent per part ofreactants, where the term reactants is used to describe the hydrolyzablesilane, the hydrocarbonyl magnesium halide and the tertiary amine. Theconditions under which the reaction will proceed will vary again withinextremely wide limits, e.g., from room temperature up to the boilingpoint of the particular solvent employed. For convenience, however, Iprefer to carry out the reaction at the reflux temperature of thesolvent, i.e., about 35 C., since the refluxing of the reaction mixtureinsures thorough agitation of the reactants and thus facilitates thereaction. Generally, the reaction is carried out at atmospheric pressurealthough it may be carried out at either subatmospheric orsuperatmospheric pressures. No particular advantage is gained by the useof other than atmospheric pressure.

The following examples are illustrative of the practice of my inventionand are not intended for purposes of limitation.

Example I A Grignard reagent was prepared by reacting equimolar amountsof magnesium and methyl bromide in about 2 parts by weight of diethylether based on the weight of the magnesium and methyl bromide. Thisresulted in a solution of methyl magnesium bromide in ether. ThisGrignard reagent was added to a solution containing equimolar amounts ofB-cyanoethylthrichlorosilane and pyridine in diethyl ether, with theether being present in an amount equal to about 1.75 parts by weight perpart by weight of the silane and pyridine. The Grignard reagent wasadded over a three hour period and regulated so that the total moles ofmethyl magnesium bromide added was equal to the number of moles of thesilane. After completing the addition, the resulting mixture wasrefluxed for one and one-half hours and then stirred overnight at roomtemperature. This resulted in a liquid containing a precipitate. Afterremoving the precipitate, the solvent was stripped off, the residue wasvacuum distilled, and the material boiling between 78 to C. at 4.5 mm.was collected. This distillate contained some unreactedfl-cyanoethyltrichlorosilane as well asmethyl-p-cyanoethyldichlorosilane, dimethyl-fi-cyanoethylchlorosilaneand trimethyl-fl-cyanoethylsilane. Since these materials are not easilyseparated by rectification, they were converted to the correspondingethoxy derivatives by adding substantially equal parts by weight of thechlorosilanes, anhydrous ethanol, and pyridine to about two parts ofbenzene and refluxing this mixture for 8 hours. At the end of this timethe reaction product was filtered and the solvent distilled off. Theresidue was then vacuum distilled, yielding a product which boiledlargely at 96 to 101 C.. at 8 mm. This distillate was carefullyfractionated to'yicld 36.9 percent of methyl-#- cyanoethyldiethoxysilanewhich boiled at 123-4255 C. at 30 mm. and which contained 15.0 percentsilicon as compared with the theoretical value of 15.0 percent silicon;26.0 percent yield of dimethyl-p-cyanoethylethoxysilane which boiled at106-108 C. at 30 mm. and contained 18.3 percent silicon as compared withthe theoretical value of 17.9 percent silicon; and 4.7 percent yield oftrimethyl-B-cyanoethylsilane which boiled at- 77-82" C. at 30 mm. Theyields described are based on the amount of Grignard reagent employed,since the Grignard reagent was the limiting ingredient in the reaction.Thus, it is seen that the reaction resulted in 67.6 percent yield ofproducts in which a methyl group was substituted for a silicon-bondedhalogen group.

When the procedure described above was repeated except that no tertiaryamine was present in the reaction mixture, the maximum yield ofB-cyanoethylsilanes containing silicon-bonded methyl groups was 14percenLifla dicating that the addition of the tertiary amine, pyridine,to the reaction mixture resulted in an almost fivefold increase in theyield of product.

Example 2 Over a one hour period, a solution of methyl magnesium bromidein 2.4 parts by weight of diethyl ether was added to an equimolarmixture of ,B-cyanoethyltrichlorosilane and pyridine in 1.6 parts byweight of di ethyl ether. The number of moles of methyl magnesiumbromide added was equal to the number of moles of the silane. Afterrefluxing this mixture for two hours, hydrogen chloride was bubbled intothe reaction mixture and the resulting pyridine hydrochlorideprecipitate was filtered oif. After distilling ofi the ether at 4.5 mm.the residue was distilled at 4.5 mm. and the fraction boiling between 76and 80 C. was collected. This distillate was then fractionallydistilled, yielding about 62 percent ofmethyl-fi-cyanoethyldichlorosilane which boiled at about 84 to 86 C. at8 to 10 mm. The methyl-B-cyanoethyldichlorosilane contained about 43percent hydrolyzable chlorine as compared with the theoretical value of42.2 percent. The yield described above was based on the amount ofmethyl magnesium bromide employed.

Although the foregoing examples have not specifically illustrated all ofthe various modifications of the process of the present invention, it iswithin the skill of the art to modify my process within the limits ofpressure, temperature, reactant concentrations, and reaction conditionswhich have been previously described. In addition, the particular typesof ingredients employed in my process are also variable within widelimits. Thus, cyanoalkylsilanes other than those particularly described,Grignard reagents other than those particularly described, and tertiaryamines other than those particularly described may be employed in myprocess.

As previously mentioned, the cyanoalkylalkylsilanes of the presentinvention are useful in the preparation of organopolysiloxane fluids,resins and elastomers. These cyanoalkyl compounds may be incorporatedinto polymeric organopolysiloxanes by conventional methods. Thus, acompound such as methyl-B-cyanoethyldichlorosilane may be hydrolyzedwith other silanes such as, for example, dimethyldichlorosilane,methyltrichlorosilane or trimethylchlorosilane to form the desiredpolymeric organopolysiloxanes.

What I claim and desire to secure by Letters Patent of the United Statesis:

1. The process for substituting a hydrocarbon radical for thehydrolyzable group of a hydrolyzable silane containing both asilicon-bonded cyanoalkyl radical and a silicon-bonded hydrolyzableradical in which the hydrolyzable radical is selected from the classconsisting of halogen, lower alkoxy radicals, and acyloxy radicals,which process comprises effecting reaction between said hydrolyzablesilane and a hydrocarbonyl magnesium halide in which the hydrocarbonylgroup is selected from the class consisting of lower alkyl radicals andaryl radicals, and the halogen of the magnesium halide is selected fromthe class consisting of bromine, chlorine and iodine, in the presence ofa tertiary amine containing only carbon, hydrogen and nitrogen, therebeing employed a molar ratio of from 0.5 to less than 1 mol of thehydrocarbonyl magnesium halide per mol of the hydrolyzable silane.

2. The method of claim 1 in which the tertiary amine is pyridine.

3. The method of claim 1 in which the hydrolyzable silane isp-cyanoethyltrichlorosilane.

4. The method of claim 1 in which the hydrocarbonyl magnesium halide ismethyl magnesium bromide.

5. The method of substituting a methyl radical for at least one of thechlorine atoms of fi-cyanoethyltrichlorosilane, which process compriseseltecting reaction between fl-cyanoethyltrichlorosilane and methylmagnesium bromide in the presence of pyridine, there being employed amolar ratio of from 0.5 to less than 1 mol of the methyl magnesiumbromide per mol of B-cyanoethyltrichlorosilane.

6. The method of claim 1 in which the hydrocarbonyl magnesium halide isa methyl magnesium halide.

References Cited in the file of this patent FOREIGN PATENTS France Feb.6, 1956 OTHER REFERENCES

1. THE PROCESS FOR SUBSTITUTING A HYDROCARBON RADICAL FOR THEHYDROLYZABLE GROUP OF A HYDROLYZABLE SILANE CONTAINING BOTH ASILICON-BONDED CYANOALKYL RADICAL AND A SILICON-BONDED HYDROLYZABLERADICAL IN WHICH THE HYDROLYZABLE RADICAL IS SELECTED FROM THE CLASSCONSISTING OF HALOGEN, LOWER ALKOXY RADICALS, AND ACYLOXY RADICALS,WHICH PROCESS COMPRISES EFFECTING REACTION BETWEEN SAID HYDROLYZABLESILANE AND A HYDROCARBONYL MAGNESIUM HALIDE IN WHICH THE HYDROCARBONYLGROUP IS SELECTED FROM THE CLASS CONSISTING OF LOWER ALKYL RADICALS ANDARYL RADICALS, AND THE HALOGEN OF THE MAGNESIUM HALIDE IS SELECTED FROMTHE CLASS CONSISTING OF BROMINE, CHLORINE AND IODINE, IN THE PRESENCE OFA TERTIARY AMINE CONTAINING ONLY CARBON, HYDROGEN AND NITROGEN, THEREBEING EMPLOYED A MOLAR RATIO OF FROM 0.5 TO LESS THAN 1 MOL OF THEHYDROCARBONYL MAGNESIUM HALIDE PER MOL OF THE HYDROLYZABLE SILANE.